1. Field of the Invention
The present invention relates to a battery including a nonaqueous electrolytic secondary battery.
2. Description of the Related Art
A battery such as a nonaqueous electrolytic secondary battery includes a positive current collector and a negative current collector for electrically connecting a positive electrode and a negative electrode in a power generating element contained inside of a battery case to a positive external terminal and a negative external terminal, respectively. The current collectors are fixed to a cover for sealing an upper opening of the battery case by means such as caulking using, for example, a rivet (see, for example, Japanese Unexamined Patent Application Publication No. 2003-346882 (FIG. 1)). Moreover, there has been known a battery in which a shaft-like portion for caulking and joining a current collector to a cover is integrated with a base portion of the current collector (see, for example, Japanese Unexamined Patent Application Publication No. 2009-277604 (FIG. 2)).
The higher the occupancy of a power generating element with respect to the volume of a battery case, the higher the energy density. A cover for a conventional battery is formed into generally a flat shape. A caulking head of a rivet located inside of the battery case projects further downward of the lower surface of the cover. Therefore, it is necessary to position the upper end of the power generating element not in the vicinity of the lower surface of the cover but in the vicinity of the caulking head of the rivet disposed further below. In other words, the projection of the caulking head of the rivet unfavorably produces a dead space between the upper end of the power generating element and the lower end of the cover. In this regard, the occupancy of the power generating element with respect to the volume of the battery case in the conventional battery cannot be satisfactorily enhanced, and therefore, no high energy density can be achieved.
Like the battery disclosed in Japanese Unexamined Patent Application Publication No. 2009-277604, when the caulking and joining shaft-like portion is disposed at the base portion of the current collector, the base portion is positioned on the lower surface side of the cover. Therefore, it is necessary to position the upper end of the power generating element not in the vicinity of the lower surface of the cover but in the vicinity of the lower surface of the base portion located further below. Also in this case, a dead space is inevitably produced, and thus, the occupancy of a power generating element with respect to the volume of the battery case cannot be satisfactorily enhanced, and therefore, no high energy density can be achieved.